In chapter three it was shown that cattle-keeping requires that homesteads remain large in western Giriamaland, while high population density and land shortage in the farming east favour smaller homesteads. Eastern homesteads therefore break up at an earlier stage of their development than western ones. The split is triggered by witchcraft accusations between brothers or by sons of fathers. By contrast witchcraft accusations are more contained in the west. People of a home-stead need each other. Brothers sleeping with each others' wives, it is claimed, is their main problem, and the dire effects of this also have to be contained.

Speaking in this way gives the impression that adulterous incest and witchcraft are sharply distinguished concepts. In conversation among Giriama this is indeed the case. They will give a clear description of how each differs. In most cases which occur, too, there is no dispute as to what is witchcraft and what incest. But there are the odd cases where the one may be redefined as the other or at least may not be so clearly defined.

What does hold these ideas together, however, is an underlying concern with fertility and the health of parents and children. The concern is obviously fundamental to the continuity of any group.